1. Field
Embodiments of the present invention may relate to an airbag system for an automobile adapted to remarkably reduce the time required for detecting a crash by measuring the stress waves, which propagate very quickly through a vehicle frame after such crash to thereby deploy the airbag in a timely manner.
2. Background
An airbag system for an automobile generally comprises the following: a crash sensor for detecting a collision of the automobile; an airbag for protecting passengers from the collision; an inflator for generating gas and supplying it to the airbag; and an electronic control unit for actuating the inflator based on the signals from the crash sensor and diagnosing the airbag system.
Three types of crash sensors have been commonly used in order to detect automobile crashes. The first is an electromechanical crash sensor wherein an electrical circuit is closed by the movement of a sensing mass caused by the inertia thereof in the event of a collision. The second is an electronic crash sensor, which utilizes the unique features of an electronic circuitry such as memory and programmability, thereby implementing the criteria for identifying and discriminating signals in the event of a collision. The last is an all-mechanical crash sensor, wherein a firing pin is released so as to ignite an inflator when the impact caused by the collision is sufficiently high enough to rotate a trigger shaft beyond a predetermined magnitude. Among them, the electromechanical crash sensor has been widely used for the airbag system since its cost is relatively low and the airbag system can be fairly easily diagnosed.
FIGS. 1 and 2 are sectional views of a prior art ball-in-tube sensor 10, which is one example of the above-mentioned electromechanical crash sensor. This sensor is manufactured by Breed Automotive Corporation and includes a sensing-mass 15 such as a steel ball and a tube 14 as disclosed in U.S. Pat. No. 3,974,350.
A magnet 12, which is disposed at one end of the tube 14, attracts the sensing-mass 15 towards one end of the tube 14. Under regular driving or braking conditions (or even in minor collisions), the attractive force of the magnetic 12 prevents the sensing-mass 15 from moving. When a collision of greater magnitude occurs, the sensing-mass 15 can move away from its resting location. If the impact is sufficiently strong and lasts long enough for the sensing-mass 15 to touch the contact 13 disposed at the opposite end of the tube 14, then the sensing-mass 15 bridges two contacts 13 and thereby closes an electrical circuit. The circuit closure sends an electrical current to an inflator, thereby initiating the deployment of an airbag.
When the sensing-mass 15 moves within the tube 14, the air within the sensor flows from one side of the sensing-mass 15 to the other side through the clearance between the sensing-mass 15 and the tube 14. Such airflow generates a drag force that dampens the movement of the sensing-mass 15. The magnitude of the damping force depends primarily on the movement of the sensing-mass 15 and the tightness of the clearance. Other factors such as the amount of air behind the sensing-mass 15, pressure and temperature within the sensor also play a role in the damping phenomenon.
In the above-described ball-in-tube sensor 10, when the crash occurs, the sensing-mass 15 moves from the normal position adjacent the magnet 12 to the contacts 13 in response to the deceleration of the vehicle and against the attractive force of the magnet 12 and the drag force of the air. In such a case, it was found that it takes 10˜20 ms to detect the crash by the electric-mechanical crash sensor such as the above-described sensor 10. It was also found that it takes 40˜50 ms to fully deploy the airbag from the airbag system. Accordingly, there is a need to reduce the time required for detecting a crash so as to deploy the airbag in a timely manner.